Method of rolling sheet steel



Patented July 20, 1926.

PATENT OFFICE.

WILLIAM J'. CROWLEY, OF NILES, OHIO.

METHOD OF ROLLING SHEET STEEL.

No Drawing.

7 My invention consists in a method of procedure, and relates to the production of sheet steel of a relatively highly perfect surface finish, from a sheet or plate having a relatively inferior surface finish. This sheet or plate of inferior finish may itself be a marketable article, useful for some purposes, and my invention may be practiced upon articles prepared for or even purchased in the market; but ordinarily the sheet or plate upon which the invention is practiced is an intermediate product in a substantially continuous operation, The resultant product of my method is one which will compare favorably with what is now known as full finished sheets, full pickled sheets, automobile sheets, metal furniture sheets, or sheets. for enameling. These finishes of sheet steel have been best produced by the process of rolling common- 1y known as loose rolling. My method of procedure involves a distinct departure from the ordinary procedure in the rolling and finishing of sheets where a relatively highly perfect surface finish is required. In making sheet steel by the ordinary practice, the initial bars are first broken down, that is to say rolled to sheet form. These sheet forms are then reheated and rolled again to substantially their ultimate dimensions? In this hot rolling the ultimate size, the mill is of the character knownas a hot mill; the rolls, though cylindrical, are, relatively speaking, not highly finished superficially, and in their mounting the rolls are, relatively speaking, not positoned with minute accuracy. The jump of the rolls is relatively great, and the articles are rolled in packs of two, three, or more. When rolling sheets by the method commonly known as loose rolling, in order to prevent sticking together during the rolling process, the sheets are, as the pack is made up, dipped in a preparation of carbon, commonly called the charcoal dip or its equivalent. The surfaces of thesheets as they come from this hot-rolling operation are relatively imperfeet and marred; those surfaces which have been in immediate contact with the roll surfaces are bright, those which have been in contact with adjacent sheets are dull, but both are uneven and carry blemishes which must be removed, before the sheet can be classed in any of the commercial categories mentioned in the preceding paragraph.

Application filed January 29, 1923. Serial No. 615,748.

In order to remove such superficial blemishes, to smooth unevenness, and to obtain a dense surface with fine finish, the otherwise finished sheets are, in connection with other finishing operations, cold-rolled. The mill for cold-rolling is distinguished from the hot mill, in that the rolls should have highly polished surfaces, and they are very accurately positoned in their mountmg. The jump of the rolls is more narrowly limited, and the sheets are put through one by one. Ordinary practice requires repeated passage through cold rolls, and box annealing before or between or after coldrolling steps is usual, or box annealing may be repeated with cold rolling between.

My departure from the usual procedure outlined above begins at the point where in the usual procedure the hot rolling to or substantially to ultimate size is approaching completion. I there stop hot rolling, shear off end and side scrap, then separate the sheets, reheat them, and roll them one by one in a mill which, since it rolls the material hot, must be termed a hot mill, but which has at the same time these characteristics of a properly cared-for cold mill,- the roll surfaces are highly polished, the rolls areaccurately positoned in their housings one relatively to the other, and the rolls are adjusted to allow but relatively small jump. In this hot-rolling. step surface blemishes are cured, the metal superficially consilidated, and a fine finish obtained. For some purposes the sheets require no further finishing; but subsequent rolling in cold rolls is not forbidden, and to meet more exacting requirements such further rolling-may be resorted to. But even in such further rolling, since the material is already superior in respect to surface finish, manifestly there is less work to be done, and the finishing step or steps are simpler, and less expensive.

In the practice of my invention there is direct saving of cost in tonnage produced per unit of hot mill, in time, in equipment, and in hot-mill crew wages, and there are indirect savings also. Such incidental saving is found in diminution of the number of pickling operations to which the material in course of fabrication is made subject. In the usual procedure it is deemed necessary to pickle the bar before breaking down, and again to pickle the break-down before hot-rolling to size. I find that in following the procedure in which the sheets are hot rolled singly between polished rolls, inthe manner already indicated, both these pickling operations may be omitted, It will sufice instead to pickle the sheets just. before heating and rolling them one by one between polished rolls. Whatever surface blemishes consequent upon failure to pickle in the usual way might remain in the product of the usual procedure, are eliminated in the hot rolling singly between polished rolls, which characterizes my invention. An ultimate pickling of the sheet after the last hot-rolling steps have been taken is of course necessary in any case, in preparation for highly finished surface, but inthat particular my procedure is in no way prejudiced.

Another source 'of incidental saving is this,l have spoken of the necessity, in the ordinary operation of hot rolling sheets, in which the resultant surface is to be relatively free from blemishes, of dipping the sheets in a preparation of carbon,before they are made up into packs for the last stages of hot rolling. That dipping is, in the practice of my invention, rendered unnecessary; for such surface blemishes as may ensue upon the sticking together and tearing apart of sheets rolled in packs-blemishes of such magnitude as are not easily and surely eradicable in the usual finishing operation of cold-ro1lingare readily eradicated in that step ofhot-rolling the sheets one by one which characterizes procedure according to my invention.

Speaking more minutely of the mill in which my invention centers, the mill in re spect to finish of roll surface and in respect to roll mounting resembles a cold mill. The rolls of a hot mill are carefully turned, and in practice the desired condition of surface is maintained by occasional grinding or scouring by rotation of the roll in contact with a block of abrasive, commonly carborundum. But the roll surfaces are such as to leave the sheet surfaces scored to such a degree as to render subsequent surface finishing necessary. The rolls of a cold mill are not only carefully turned or ground; they should be highly polished. And the surface polish is maintained by occasional rotation in contact with a somewhat elastically mounted block of abrasive, with the application of a lubricant, palm oil, or its equivalent.

A roll for a hot mill is ordinarily made of gray iron, chilled, not so high in carbon and accordingly not so hard as a roll for a cold mill, and the chill formed superficially upon a hot roll is not ordinarily so deep as upon a cold roll. In the practice of my invention the rolls for hot rolling singly will, in respect to quality of iron and depth ,of chill, be suited to their purpose. I believe this will be served best by forming the rolls of iron intermediate in hardness, between that ordinarily used in casting hot rolls and that ordinarily used in casting cold rolls, and by producing a chill of intermediate depth. But it will of course be understood that I do not mean to limit my invention in these particulars,--only to indicate what I believe to be good practice.

In the mounting of hot rolls the upper roll of the stand is screwed down by single screws in each housing, advancing vertically in lines coincident with roll axis. In a cold mill the upper rolls are screwed down by a pair of screws in each housing advancing vertically, one on either side of the line of roll axis, and in consequence the rolls are susceptible to more accurate positioning and being positioned are more securely held in position, one relatively to the other, than in the hot mill. In this respect in the practice of my invention, 1 preferably mount and adjust the rolls of the mill in which my invention centers after the manner employed in cold mills. I

It remains to outline the usual procedure in rolling steel sheets of highly finished surface by the loose rolling method, and to compare with such usual procedure, the procedure in practicing my invention.

The material commonly used is the product of the open-hearth furnace. Beginning with such material in the form of bars, the usual procedure is as follows,.

1. The bars are initially pickled, washed, and dried.

2. The cleaned bars are heated to rolling heat, and broken down; that is to say, rolled and reduced in thickness, from the initial thickness of the bar to say a thirtysecorid of an inch. The bars are ordinarily broken down two by two, and toward the end of the breaking-down are superposed and rolled double.

3. The articles now brought to the form of sheets a thirty-second of an inch in thick ness, more or less, and in mill parlance called the break-down, are allowed to cool and when cold are pickled a second time, washed, and dried.

d. The sheets are gathered in packs of two, three or more, and, in gathering, those sheets which are to be interior sheets of the pack are dipped injhe charcoal dip.

5. The gathered packs are heated again to rolling temperature and rolled in the ordinary hot mill, to or approximately to their ultimate dimensions. (There is of course, attenuation of relatively small magnitude in the ensuing cold rolling.)

6. The packs are cooled and when cold are sheared and opened. and for a third time the sheets are Pickled. washed, and dried. 4

lid

Finishing follows. The finishing operations typically may include,-

Annealing,

8. Cold rolling in one or more roll passes,

9. Annealing again, and, finally,

10. Cold rolling.

The order of the steps 6 to 10 may be altered, depending upon the use for which the resultant sheets are intended and upon the practice of individual manufactures, but all highly finished sheets, after hot rolling, shearing, and opening, must have one pickling, two or more passes in polished cold rolls, and one or more annealings.

In the practice of my invention I dispense with steps 1, 3, and 4 of the procedure outlined above, I modifiy slightly step 5, I introduce after step 6- a new step, and, in consequence, the finishing operations are simplified; the amount of finishing work to be done is less. The number and general character of the finishing steps may or may not be less. My procedure may be as follows,

1. The unpickled bar, with its coating of scale upon it is heated and broken down.

'01: course my invention does not forbid the initial pickling, nor any subsequent pickling, but in the practice of my invention I find the initial pickling and the pickling of the break down unnecessary, and, therefore, preferably omit both.

2. The break-down, still unpickled, is gathered into packs, heated and rolled in the usual ho't mill. As I already have explained. the dipping of the sheets in the charcoal dip is in the practice of my invention rendered unnecessary. It may of course be restorted to, if under usual circumstances, or for any reason it be found desirable. In this hot rolling to approximately ultimate dimensions I so far modify the usual procedure as to make. allowance for that new step in which my invention centers, and carry the attenuation forward to slightly less than the usual extent. For

, example, if in the usual operation a sheet is in this hot-rolling step brought to a length of 96 inches, I, in order to reach a product of the same ultimate dimensions, may roll to a length of say 90 inches.

3. The packs are allowed to cool and when cold are sheared and opened and now for the first time, preferably, the articles are pickled, washed, and dried.

4. The new step follows. The separated sheets are heated to rolling temperature and passed one by one through the mill which,

as above explained, differs from the ordi-- nary hot mill, in that the rolls are polished, like the rolls of a properly cared-for cold mill, and are accurately positioned and secured in their housings, similarly as in the roll mounting in a cold mill. The hot'rolling step just described, in which my invention centers, may be accomplished in any preferred number-of roll passes. I find three such roll passes to be adequate.

5. The articles after this last hot-rollingand blemishes and possess a fine finish. For

some uses they are sufficient as they are,

without any further treatment whatever.

For other purposes cold rolling or equivalent finishing may be practiced, although, as I have said, the cold-rolling operation upon these sheets of mine is, as compared with the usual cold-rolling operation, a relatively simple matter. Typically, I proceed with a finishing operation by,

7. Cold rolling, one or more passes,

8. Annealing in boxes, and

9. Cold rolling, one pass.

Sheet steel highly finished on both surfaces is greatly in demand, and for many uses,for making metal furniture, for making enameled ware, enameled tables, enameled signs and the like, for stove work, and notably for making automobile bodies, and for other uses. It will be remarked of the uses particularly named, most of them involve a covering of the metal surfaces with viscid or paint-like character, applied in a spray on by brush, or perhaps a Japan of one kind or another. In either case, in order to attain desired quality in the finished article, the surface of the steel sheet must be of relatively high grade and free of blemish. For some of these uses steel sheets rolled hot and singly between polished rolls, in the manner here described, will be found to be adequate; for others, in which requirements are more exacting, the so-rolled sheets may be subjected to an additional finishing operation, which ordinarily will be cold-rolling or annealing or both. But, as I have explained, such finishing operation, when resorted to, is a simpler matter and the product superior, in consequence of the antecedent hot rolling singly between polished rolls,

sists in subjecting the break-down in packs to the normal hot-rolling operation, inter- .sheet steel to predetermined size which con- 1 mitting the hot-rolling operation whilethe degree of extension is less than requisite for normal cold-roll finishing, then shearing and opening the packs, reheating the sheets, and rolling them again singly at hot-rolling tem perature between rolls having the surface character of cold rolls.

2. The method of rolling sheet steel herein described which consists in breaking down the unpickled bars, rolling in packs the unpickled break-down, shearing and opening the packs and pickling the sheets, and then heating and rolling the sheets singly at hotrolling temperature between polished rolls.

3. The method of rolling sheet steel herein described which consists in breaking down the unpickled bars, rolling in packs the unpickled break-down, shearing and opening the packs and pickling the sheets, and then, in continuous operation and one by one, heat-- ing to hot-rolling temperature, rolling between polished rolls, and annealing the sheets.

4. The method of rolling sheet steel herein described which consists in breaking down the unpickled bars, rolling in packs the unpickled break-down, shearing and opening the packs and pickling the sheets, heating the sheets and rolling them athot-rolling temperature between polished rolls, annealing, pickling again, and finishing the sheets.

In testimony whereof I have hereunto set my hand.

' W. J. CROWLEY. 

